In the offshore industry there is a need for underwater pipelines. These underwater pipelines may be provided by joining pipe sections together in a substantially vertically position to form a pipeline which is lowered from a vessel to an underwater bottom. In such a pipe laying method, which is commonly referred to as a J-lay method, a plurality of pipe sections, welded to one another, together forming a part of the pipeline, hang down from a vessel in a substantially vertical direction, where an upper end of the most recently joined pipe section is to be welded to a lower end of a new pipe section being lined up above said upper end.
In a specific embodiment of the J-lay method, at least one end of the pipe sections is provided with a collar for easier handling of the pipe sections. Upon completion of a weld, the end of the pipeline is gripped by the collar with a head clamp and lowered to just below the welding position to prepare for a new pipe section to be arranged above the upper end of the lowered pipeline.
The welding of two pipe sections requires exact positioning of the welding equipment, in particular the welding heads with respect to the weld gutter. In a known welding system, a guiding device is provided which guiding device is configured to revolve welding equipment about the axis of the pipe sections. The guiding device comprises a clamping band which is placed about the pipe section and supports one or more carriers each carrying one or more welding heads. The carriers are movable with respect to the clamping band and configured to revolve the welding heads about the circumference of the pipe section substantially in line with the weld gutter.
An example of the known guiding device is for instance disclosed in WO 2004/071702, the contents of which are herein incorporated by reference. In the guiding device of WO 2004/071702 two separate carriers are provided to revolve two welding heads at different speeds about a pipe section to provide a weld between the two pipe sections.
During placement of the clamping band on the respective pipe sections, the clamping band has to be accurately positioned with respect to the end of the pipe section on which it is mounted so that the task zone of the equipment carried by the clamping band is lined up with the weld gutter. This positioning is carried out by manually adjusting the position of the clamping band to the correct location before definitive clamping of the clamping band. The manual positioning of the clamping band requires a considerable effort and is time-consuming.
After the welding of two pipe sections, the resulting weld has to be inspected. For this inspection a separate welding inspection unit is used. In the known method, the guiding device of the welding heads is removed from the pipe section, and a new guiding device for the inspection equipment is clamped on the pipe section. The guiding device of the inspection equipment comprises a clamping band which supports a movable carrier which may revolve around the pipe to inspect the weld.
Usually, the clamping band of the inspection equipment guiding device has to be placed at a different distance from the weld than the clamping band of the welding heads guiding device, as the working height of the respective equipment is not the same. However, when placing the clamping band of the inspection equipment guiding device the original weld gutter is not exactly known which makes correct placement more difficult. In practice, prior to welding a scribe line is made on the pipe section at a certain distance of the weld gutter to indicate the exact location of this weld gutter. However, it is time consuming to make a scribe line prior to welding and to exchange the welding equipment guiding device for the inspection equipment guiding device after welding.